The use of sulfur in dermatological products has been known for many years. The sulfur may be useful on dermatological disorders such as acne vulgaris, acne rosacea, mite infestations and other conditions. Sodium sulfacetamide is also often used in combination with sulfur for the treatment and/or prevention of such dermatological disorders. However, there are several problems with sulfur formulations in the prior art.
First, sulfur and sodium sulfacetamide may degrade into malodorous components, such as sulfanilamide. Chemical and physical stability for sulfur and sodium sulfacetamide compositions has been difficult to achieve. Many sulfur compositions degrade, turn color and become malodorous in a relatively short time, which is undesirable to consumers.
Patients frequently use sulfur and sodium sulfacetamide compositions on the face and other skin. In order to promote compliance, it is desirable to have non-malodorous and aesthetically pleasing compositions.
Sulfur and sodium sulfacetamide compositions in the art have employed gums, clays, silicates and other sorptive materials in order to promote stability of the sulfur and sodium sulfacetamide. However, the stability provided by these sorptive materials is limited and often not conducive to cleanser compositions. In certain embodiments without limitation, the present invention does not comprise gums, clays, silicates and other sorptive materials.
Sorptive materials are defined to include those materials which, when applied topically to the skin, absorb irritants, including but not limited to sweat, sebum, oil and dirt, from the skin.
Sulfur and sodium sulfacetamide compositions in the art frequently use emulsifiers with HLB (“Hydrophilic Lipophilic Balance”) numbers of around 30 or combined HLB numbers of about 30 or higher. However, chemical and physical stability appear to suffer in these compositions.
HLB Numbers
An HLB number referred to in this specification is calculated in the manner developed by William Griffin and used by ICI Americas, Inc. (“ICI”). It is well-known in the art and conventionally calculated and published. See, Griffin, W. C. “Classification of Surface-Active Agents by HLB,” J. Soc. Cosmet. Chem. 1, 311-326 (1949); and Griffin, W. C. “Calculation of HLB Values of Non-Ionic Surfactants,” J. Soc. Cosmet. Chem. 5, 249-256 (1954) (incorporated herein by reference). ICI has published numerous reference materials regarding the HLB number.
The HLB number is an indication of the hydrophilic portion of an emulsifier molecule. The HLB number indicates the polarity of the molecules in a 1-20 range, and the number increases with increasing hydrophilicity. HLB numbers are usually calculated or obtained experimentally for nonionic surfactants. However, HLB numbers are often assigned up to 40 for ionic surfactants. These numbers over 20 are relative or comparative numbers, which are not based on strict mathematical formulas, but are conventionally known and used. If a nonionic emulsifier were 100% hydrophilic, the HLB number would be 20, because the factor ⅕ is used (e.g. ⅕ of 100). An emulsifier that is lipophilic has a HLB number of below about 9 and one that is hydrophilic has a HLB number of above about 11. Those in the range of about 9-about 11 are indeterminate. ICI publishes the HLB number of many of its emulsifiers, and the other are calculable using the ICI method, which is known in the art. ICI also set forth the following information regarding the uses of emulsifiers.
TABLE 1HLB RangeUse4-6Water/Oil Emulsifiers7-9Wetting Agent 8-18O/W Emulsifiers13-15Detergents10-18Solubilizers
When two or more emulsifiers are combined, the resulting combined HLB number is calculated by adding (the percentage of emulsifier(1) multiplied by HLB(1)) and (the percentage of emulsifier(2) multiplied by HLB(2)). This can be calculated for any number of emulsifiers which are combined.
HLB numbers can help predict what are the appropriate emulsifiers to use in a particular instance. The chemical type of the emulsifier also plays an important role in the most effective emulsifiers as is understood by one of ordinary skill in the art. In fact, the most stable emulsifier systems usually consist of combinations of two or more emulsifiers, a portion with lipophilic tendencies and a portion with hydrophilic tendencies.
ICI also provides the following guidance on dispersibility in water.
TABLE 2HLB by DispersibilityHLB RangeNo dispersibility in water1-4Poor dispersion3-6Milky dispersion after6-8vigorous agitationStable milky dispersion 8-10Translucent to clear10-13dispersionClear solution13+
Preparing stable emulsions, as is known to those of ordinary skill in the art, is an inexact and time-consuming process. To date, sulfur and sodium sulfacetamide compositions, which are emulsions, and particularly cleansers, have shown a tendency to be unstable, physically and chemically. The present invention achieves a surprising stability for such compositions, along with the additional benefit of being aesthetically pleasing and dermatologically desirable.